Multiplexing systems can be defined as digital based electronic schemes for sequentially accessing a variety of remote stations or nodes. Such systems comprise a central control unit connected to a plurality of remote nodes via a bi-directional transmission line. The signals communicated between the central control unit and the remote nodes take the form of electronic bits of information which define either a logic "0" or "1" binary state.
In a time division multiplex system the communicated data is defined by time windows also known as slots or frames. Each bit position within a time window has a predefined meaning which can change based on the addition of complex flagging bits or patterns that may sandwich the data signal bits. An additional or different kind of flag bit may also be included to indicate that more signal bits are coming for a particular frame and/or that selected bit positions are to be redefined.
U.S. Pat. No. 4,311,986 issued to Yee describes a multiplex system in which pulse width modulation is utilized to create a unique address for each remote station in the system. The central processor sends out interrogation pulses of a controlled width, wherein the width identifies the specific remote station which is the intended recipient of the pulse. Each remote station, when it receives an interrogation pulse of the appropriate width, responds by supplying a return pulse on the bus with a delay that encodes the desired information. In the Yee system, the variable width interrogation pulse identifies the remote station by the width of the pulse.
It is an object of the present invention to eliminate the need for complex flag bits and pulse widths surrounding the transmitted data signals between a control unit and a remote node in a multiplex system.
It is a feature of the present invention to provide selected periods of inactivity on a bi-directional transmission line in order to define the transmission mode of data signals being sent over the line.
It is a further feature of the present invention to provide selected periods of inactivity on the bidirectional transmission line in order to define the direction of transmitted data as originating from a control unit or from one of a plurality of remote nodes.
It is thus an advantage of the present invention that when transmitted data signals are defined and controlled by selected periods of inactivity on the transmission line, there is an increase in signal transmission throughput because of the elimination of complex flag bits.